D. Goddard, J.I. Paul, S.E. May
National Nuclear Laboratory
Uranium nitride (UN) is receiving considerable interest as a potential fuel for advanced Generation IV reactors, where the high density, high melting temperature and excellent thermal properties are attractive. Many routes have been demonstrated for the fabrication of UN, most notably by carbothermic reduction under nitrogen and nitriding of powdered uranium metal or hydride. The preferred route will depend on the feedstocks and whether the reactor is operating an open or closed fuel cycle. For open cycles utilising an enriched UF6 feedstock it would be beneficial to develop a more direct conversion route from UF6, as is the case for UO2 fuels. The Advanced Fuel Cycle Programme, a collaboration between NNL and the Department of Business, Energy and Industrial Strategy, is investigating ammonia-driven conversion of UF6 to uranium nitrides. In doing so intermediate ammonium uranium fluoride compounds will be formed, of which at least nine different compositions and polymorphs are known, with NH4F:UF4 ranging from 4:1 to 1:3. In this work we report on the synthesis and characterisation of the majority of these compounds through anhydrous and aqueous reaction schemes. Thermogravimetric analysis has also been carried out to determine the temperatures of reaction sequences starting with (NH4)4UF8 and finishing with UF4. The results will help to inform planned work on UF6-ammonia reactions and subsequent conversion to nitrides.
Event Timeslots (1)
Tuesday – 14th September 2021